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Solar System Ices and Icy Bodies

Researchers in this field seek to better understand the properties of the surfaces, interiors and atmospheres of the many icy bodies in the solar system, and related small bodies such as asteroids and Near Earth Objects (NEOs). These efforts involve space and ground-based observations, theoretical modeling, data analysis, and laboratory experiments.

Scientists are all but certain that Europa has an ocean underneath its icy surface, but they do not know how thick this ice might be. This artist concept illustrates two possible cut-away views through Europa's ice shell.

Ices are found in numerous locations in the universe and play a key role in the chemistry, physics and evolution of bodies within planetary systems. Researchers in this area represent a diverse range of backgrounds and expertise focused on investigating the whole range of ices in the solar system. There is a strong focus on the icy moons of Jupiter and Saturn, such as Europa, Ganymede, Enceladus, Titan, and Triton. Also of interest are comets, Kuiper Belt Objects (KBOs), NEOs and asteroids, and the polar regions of Mars. Research in this field contributes to our understanding the formation and evolution of icy bodies and the Solar System as a whole.

Selected Research Efforts

Thermophysical, Rheological and Mechanical Measurements on Icy Compositions with Application to Solar System Ices
The purpose of the research project is to experimentally determine the thermophysical, rheological, and mechanical properties of icy materials (ices and candidate cryolavas) over a cryogenic temperature range (80 K < T < 300 K), which is applicable to outer solar system objects such as Jupiter’s and Saturn’s satellites, as well as Mars polar caps and terrestrial ice sheets. Using these material properties, modeling of satellites’ thermophysical, dynamical, and geological evolution was conducted, in order to support the following science objectives: (1) to model the physical mechanisms that are responsible for the cryovolcanic activity observed on Titan or inferred on other outer-planet icy worlds; (2) to model, for the first time, the geophysical response of icy satellites to tidal excitation; (3) to model the geological processes of icy satellites; and (4) to determine the spectroscopic properties of ice samples in order to match the laboratory data with spacecraft observations. The research strives to understand the evolutionary history of planetary ices, in terms of the geophysical and geologic processes that have occurred in icy worlds around the solar system.

Physical Chemistry of Planetary Ices
The outer solar system is populated by ice-rich bodies: comets, Kuiper Belt Objects, centaurs, “primitive” asteroids, and icy planetary satellites. The research objective in this project is to study and develop an understanding of the physical chemistry of ices of the outer solar system.

Infrared spectra of unirradiated (blue) and irradiated (red) water-ice film containing isobutane. Note production of alcohols and CO2.

The outer-planet-satellite bulk surface icy compositions are predominantly water ice, with small amounts of co-condensed simple molecules such as NH3, CO2, CO, N2 and CH4, depending upon the condensation distance from the sun in the primordial solar nebula. It is these outer surfaces that respond to particle and photon bombardment from the sun, the solar wind, and charged particles trapped in local planetary magnetospheres, in addition to thermal cycling. The focus is on larger bodies of the outer solar system such as the Jovian and Saturnian icy moons. Inorganic, organic and biological compounds may be present on/in surface ices. Such species could be delivered to icy surfaces through meteoric impacts or, on bodies such as Europa and Enceladus, potentially through active chemistry in subsurface liquid water. The research investigates the temperature-dependent chemical pathways available to mixtures of ices and inorganic/organic compounds subjected to energetic stimuli relevant to the outer Solar System.

This investigation includes performing a series laboratory experiments designed to elucidate the physical chemistry within ices relevant to icy solar system objects. The basic experimental approach is to engineer ice analogs constrained by model predictions and observations of solar system ices (composition, temperature, phase, structure, etc.). Once formed, the ices are systematically and quantitatively subjected to thermal cycling, UV photon irradiation, electron irradiation, etc. A number of analytical methods are applied to unravel the chemical and physical changes occurring in the samples. The investigation addresses questions such as: What are the essential chemical/physical properties of ices under conditions relevant to outer solar system ices? What kind of chemistry can occur in these ices? This project is providing precise, accurate, and quantitative descriptions of the physical chemistry that occurs in outer solar system ice analogs in order to lay a solid foundation for ground-truth understanding of observations obtained by JPL/NASA missions, e.g., Galileo ISS, UVS, NIMS & Cassini ISS, VIMS and UVIS observations, and by ground-based facilities including Palomar Observatory, Table Mountain Observatory, NASA’s Infrared Telescope Facility, Arecibo, and Goldstone.

Radar Observations of Near-Earth Objects
Near-Earth Objects (NEOs) are asteroids or comets that approach or cross the Earth’s orbit. They represent a potential hazard if they are both sufficiently large and on an impact path to Earth. JPL has led efforts to discover and track NEOs, and it is currently performing radar investigations of the properties of NEOs at radio telescopes in Arecibo, Puerto Rico, and at the Goldstone Deep Space Network in the Mojave Desert. These efforts are designed to understand the physical properties of NEOs such as their composition, roughness, size and gross structure, mechanical strength, dynamical properties, and surface texture. Many binary NEO systems have also been discovered with radar images. Kindred studies on the optical spectra and rotational states of NEOs are performed at Palomar Mountain and Table Mountain Observatory by JPL scientists. A better understanding of the nature of NEOs reveals their origins, their collisional history, and the conditions under which they formed. Radar studies are also key for characterizing these bodies for further exploration by robotic spacecraft, including in situ samplers, and by astronauts.

A radar image of 1998 QE obtained by the Goldstone 70 meter tracking telescope, which is part of the Deep Space Network. A binary companion is clearly visible in the image. The asteroid was about 6 million kilometers from Earth when this image was obtained.